1. Field of the Invention
The present invention relates to an optical information recording apparatus, an optical information recording method, and a signal processing circuit and, in particular, to an optical information recording apparatus, an optical information recording method, and a signal processing circuit for effectively optimizing a recording condition for a medium having different recording characteristics in the inner and outer peripheries thereof.
2. Description of the Related Technology
The level of compatibility between optical information recording mediums including a CD-R (compact disc-recordable) and DVD-R (digital versatile disk-recordable) (hereinafter simply referred to as a “medium”) and a recording apparatus (hereinafter referred to as a “drive”) varies depending on different combinations thereof. This may be caused by a factor of the medium in that the optimum recording condition varies depending on the type of recording material of the medium and variation in a formed layer at assembly time and a factor of the drive in that the optimum recording condition varies depending on the types of a pickup and a semiconductor laser of the drive and part-to-part variation in assembly at fabrication time. In fact, an optimum recording condition for each combination of a medium and a drive is determined by any combination of the above-described factors.
Accordingly, a method is proposed in which a medium stores identification (ID) information for a drive to identify the type of the medium and a drive stores recording parameters prepared for each type of the medium in advance. When recording information on the medium, the drive reads the ID information from the medium loaded on the drive and uses the recording parameters (also referred to as a “writing strategy”) associated with the ID information.
According to this method, substantially optimum recording parameters can be selected for a known medium that is verified in advance. However, there is a possibility that the stored recording parameters cannot support an unknown medium that is not verified in advance. Additionally, even for a medium that is verified in advance, when a recording environment (e.g., a recording speed, a disturbance, or deterioration with age) changes, the stored recording parameters cannot always support the medium.
A method for supporting an unknown medium is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2003-30837 and Japanese Unexamined Patent Application Publication No. 2004-110995. Paragraph 0020 of Japanese Unexamined Patent Application Publication No. 2003-30837 includes a statement that “ . . . A phase error between the signal and a channel clock is detected for each recording pattern. A recording compensation parameter controller 12 optimizes the laser emission waveform rule on the basis of the detection result from a phase error detection unit 11 . . . ”. That is, a method is disclosed that detects a phase error and corrects the phase error by comparison with a channel clock.
In addition, paragraph 0024 of Japanese Unexamined Patent Application Publication No. 2003-30837 includes a statement that “ . . . Subsequently, a test pattern for determining the laser emission waveform rule is recorded. The area in which the test pattern is recorded is then played back and a relationship between a prepared laser emission waveform rule and an amount of the phase error is examined. That is, an amount of the phase error for each combination of the length of a mark and the length of a space immediately before the mark is measured. A laser emission waveform rule that causes the amount of the phase error to be zero is estimated on the basis of the measured amount of the phase error to determine a desired laser emission waveform rule . . . ”. That is, a method is disclosed that measures an amount of the phase error for each combination of a mark and a space to estimate a laser emission waveform rule that causes the amount of the phase error to be zero (refer to FIGS. 8 and 12).
According to the method described in Japanese Unexamined Patent Application Publication No. 2003-30837, correction is carried out on the basis of the phase error of a recording pattern. Accordingly, this method is effective for optimizing a strategy.
However, according to the method described in Japanese Unexamined Patent Application Publication No. 2003-30837, like a known method, only a strategy prestored in a drive is finely tuned. Accordingly, it is difficult to obtain superior recording quality from a medium that is not adaptable to the prestored strategy.
Additionally, paragraph 0045 of Japanese Unexamined Patent Application Publication No. 2004-110995 includes a statement that “ . . . A top pulse corresponding to 3T period and a non-multi pulse corresponding to 8T period are integrally (continuously) generated . . . ”. Furthermore, paragraph 0046 of Japanese Unexamined Patent Application Publication No. 2004-110995 includes a statement that “ . . . The laser power of the light pulse is controlled in two stages. When a ratio of laser power (crest value of the top pulse) Ph to laser power (crest value of the non-multi pulse) Pm is optimal, the optimum power is obtained . . . ”. This statement suggests that optimizing the ratio of Ph/Pm is effective for increasing the compatibility.
However, according to the method described in Japanese Unexamined Patent Application Publication No. 2004-110995, as described in paragraph 0067 of Japanese Unexamined Patent Application Publication No. 2004-110995, initial values of Ph and Pm are temporarily set, and subsequently, the ratio of Ph/Pm is determined. Accordingly, as in Japanese Unexamined Patent Application Publication No. 2003-30837, it is difficult to obtain superior recording quality from a medium that is not adaptable to the temporary setting values.
Additionally, information is recorded on an optical information recording medium, such as an optical disk, by modulating data to be recorded with an 8-14 modulation (EFM) method or an 8-16 modulation method, generating recording pulses on the basis of the modulation signal, controlling the laser beam intensity and laser beam emission timing on the basis of the recording pulses, and forming recording pits on the optical disk.
Since the recording pits are formed by using thermal heat generated by laser irradiation, the recording pulses need to be set while taking into consideration a thermal storage effect and thermal interference. Accordingly, in the known drives, various parameters for setting the recording pulses are determined for each type of an optical disk in the form of a strategy. To record information on an optical disk, an optimum strategy for a recording environment is selected from among a plurality of the strategies.
The strategy depends on not only individual variability in an optical information recording apparatus, such as variation in a spot diameter of a pickup and variation in precision of a mechanism, but also on a manufacturer of an optical disk used for recording and playback and a recording speed. Therefore, setting an optimum strategy increases the recording quality.
Thus, a technique has been proposed in which the optimum strategy for an optical disk of each manufacturer is determined and prestored in a memory. When recording information on an optical disk, the name of the manufacturer recorded on the optical disk is read out of the memory to use the optimum strategy corresponding to the readout name of the manufacturer.
However, according to this technique, optimum recording can be carried out for an optical disk whose manufacturer name is recorded in the memory, but not for an optical disk whose manufacturer name is not recorded in the memory. In addition, even for an optical disk whose manufacturer name is recorded in the memory, optimum recording cannot be carried out if the recording speed is different.
Accordingly, test recording is carried out for each recording condition in advance, as discussed in Japanese Unexamined Patent Application Publications No. 5-144001, 4-137224, 5-143999, and 7-235056. An optimum strategy is then determined on the basis of the test recording so as to support a variety of types of optical disk. However, according to the technique discussed in Japanese Unexamined Patent Application Publications No. 5-144001, 4-137224, 5-143999, and 7-235056, test recording is required before starting to record information, and therefore, the strategy cannot be corrected simultaneously with the information recording. Accordingly, it is difficult for this technique to correct the strategy if the optimum condition for the inner periphery is different from that for the outer periphery.
To solve this problem, that is, the problem that the recording quality differs at the inner and outer peripheries because the recording characteristics of an optical disk slightly vary from the inner to outer peripheries and some recording units have different recording speeds at the inner and outer peripheries, Japanese Unexamined Patent Application Publication No. 53-050707 discloses a technique that reduces the difference in the recording quality between the inner and outer peripheries by controlling the output of the laser. Japanese Unexamined Patent Application Publication No. 53-050707 discloses a technique that automatically optimizes the output of laser by detecting the change in the intensity of an auxiliary beam. This technique is referred to as an “OPC”.
The above-described OPC is a technique called a running OPC that controls the power in real time. Since the running OPC can determine correction conditions using a statistical index, such as an asymmetry value, real-time correction in which the correction is carried out during recording can be provided. To correct a pulse width and a pulse phase condition, an amount of shift between a recording pulse and a pit formed on an optical disk needs to be detected. However, it is difficult for the known OPC to detect the amount of shift.
Accordingly, to correct the pulse conditions in real time, a technology that detects the positions and lengths of a pit and a space during recording is required. As one of approaches to provide this technology, Japanese Unexamined Patent Application Publication No. 51-109851 discloses a technology that plays back the location that is substantially the same as the recorded location. However, although this technology is applicable to magnetooptical recording, it is difficult to apply this technology to optical recording that does not use magnetic recording. That is, since, in magnetooptical recording, information is recorded using magnetic modulation, the output of laser is not modulated. In contrast, since, in optical recording, information is recorded using laser output modulation, the laser output modulation disadvantageously affects the playback of the information.
The following Patent Documents disclose technologies to solve this problem: Japanese Unexamined Patent Application Publications No. 1-287825, 7-129956, 2004-22044, and 9-147361. According to Japanese Unexamined Patent Application Publication No. 1-287825, different beams are emitted to an unrecorded area and a recorded area to obtained first and second signals. The playback signal is generated by dividing the second signal by the first signal. This technology can correct the distortion of the waveform of the playback signal caused by the laser beam intensity modulation during recording.
According to Japanese Unexamined Patent Application Publication No. 7-129956, a playback signal is obtained while canceling the modulated output by the laser output appropriately amplified by an auto gain control (AGC) using the reversed phase clock.
According to Japanese Unexamined Patent Application Publication No. 2004-22044, the distortion of a playback signal due to the variation of a waveform of a recording pulse is canceled by a signal which corresponds to the variation of a waveform of a recording pulse and which is generated by a delay inversion equivalent circuit.
In the technologies discussed in Japanese Unexamined Patent Application Publications No. 1-287825, 7-129956, and 2004-22044, a modulated component is canceled by computation. Theoretically, the modulated component can be canceled. However, various problems remain for a practical application in terms of the precision of the cancellation and the computing speed.
According to Japanese Unexamined Patent Application Publication No. 9-147361, the shift occurring during recording is detected in real time by inputting a pulse delayed from a pulse used for recording and a gate signal inverted from a modulated signal into a phase comparator together with a playback pulse.
However, in the technique discussed in Japanese Unexamined Patent Application Publication No. 9-147361, since a pit is played back when a recording pulse is off, it is difficult to obtain a playback signal of sufficient quality when the output level of a sub beam is low. In particular, in a configuration that generates a sub beam for playback by dividing a main beam for recording, it is difficult to allocate sufficient power to the sub beam when the branch ratio is, for example, 20:1 or 30:1.
That is, according to Japanese Unexamined Patent Application Publication No. 9-147361, the branch ratio is 8:1. However, as the recording speed increases, the branch ratio tends to increase. Additionally, in general, the output power of a beam is less than or equal to 1 mW when a recording pulse is turned off. Accordingly, the detected intensity of reflected beam from the recording surface becomes very small when a recording pulse is turned off. If the detected intensity of the beam becomes very small, the beam is easily affected by circuit noise and medium noise, and therefore, a superior detection signal cannot be obtained.
In contrast, to detect the lengths of a pit and a space recorded on an optical disk, the following methods are known: an integration detection method using an integration value of a playback RF signal, an amplitude detection method using a first derivative value of an RF signal, and a peak detection method using a second derivative value of an RF signal.
However, in an optical recording apparatus that carries out a playback operation using a laser beam of a relatively short wavelength, since the interference between a spot and a pit does not occur for an optical medium recorded in low density, it is difficult to detect length information using the integration detection method for the RF signal.
According to the method using a first derivative value of an RF signal, if the recording power varies with the variation of a recording speed, signals digitized in the same slice level are recognized as different lengths even when pits or spaces of the same lengths are detected. To solve this problem, the slice level may be changed in accordance with a recording speed. However, it is difficult to set an appropriate slice level for each recording speed.
For example, International Publication No. WO96/24130 discloses the peak detection method using a second derivative value of an RF signal. In the method disclosed in International Publication No. WO96/24130, by differentiating a difference signal of a light detector having two areas divided by a dividing line optically perpendicular to the rotational direction of an optical medium, that is, by differentiating a tangential push-pull signal, a signal equivalent to a second derivative of an RF signal is generated. By using this signal, the edge position of a pit can be detected.
However, when a pit and a space recorded on an optical density type optical medium (e.g., a medium of a DVD class) are detected using the method disclosed in International Publication No. WO96/24130, an error occurs in a derivative value of a tangential push-pull signal from a short pit of 3T or 4T that easily causes interference. Thus, a value different from the proper value is detected.
Additionally, Japanese Unexamined Patent Application Publication No. 2002-117544 discloses a method that is an improvement of the above-described running OPC. In Japanese Unexamined Patent Application Publication No. 2002-117544, a method for detecting the optimum power using a specific pit land pattern is disclosed. However, according to the pit land pattern discussed in Japanese Unexamined Patent Application Publication No. 2002-117544, the power cannot be distinguished from an adjustment element of a pulse width, and therefore, a margin for providing the sufficient recording quality cannot be obtained. As a result, it is difficult to support high-speed recording.